1. Field of the Invention
This invention relates to methods of preconditioning a resin and to resins prepared therefrom. The invention also relates to methods of removing ionic impurities from a hydrogen peroxide solution using the preconditioned resin. The invention has particular applicability in the semiconductor manufacturing industry.
2. Description of the Related Art
Hydrogen peroxide (H2O2) is an important chemical in the semiconductor manufacturing industry. It is commonly used in solutions employed in wafer cleaning processes which are conducted in wet processing stations. For example, the well known piranha clean process employs a solution of hydrogen peroxide and sulfuric acid (H2SO4) in a ratio of 3:7. Other processes employing hydrogen peroxide solutions include, for example, the RCA SC-1 clean which involves a solution of ammonium hydroxide (NH4OH) and hydrogen peroxide in a ratio of 5:1:1, and the RCA SC-2 clean, which uses a solution of hydrochloric acid (HCl) and hydrogen peroxide in a ratio of 6:1:1.
To reduce the probability of device failure, it is important in semiconductor device fabrication that the materials which contact the wafers being treated be of very high purity. The extreme purity levels required in semiconductor manufacturing are rare and unique among industrial processes. While existing techniques of purifying hydrogen peroxide may significantly reduce the amount of contaminants, solutions of even greater purity are desirable.
Commercial grade hydrogen peroxide is generally produced by the so-called anthraquinone method. This method involves auto-oxidation of anthraquinone, which results in the presence of large amounts of organic and ionic contaminants in solution. The contaminants may either originate from the anthraquinone or from the organic solvents used in preparing the hydrogen peroxide solution from the anthraquinone.
It is conventional practice to treat hydrogen peroxide with an ionic exchange resin to remove the ionic impurities. However, anion exchange resins which have hydroxide as the ion of exchange have been found to be very reactive, thus generating a large amount of heat when utilized to purify solutions of hydrogen peroxide. To overcome this deficiency, conventionally, the hydroxide has been converted to bicarbonate through the use of solutions of ammonium bicarbonate or sodium bicarbonate. Subsequently, the resin is flushed with deionized water and utilized to treat the hydrogen peroxide solution.
There are, however, various problems associated with the use of exchange resins to remove ionic impurities from an aqueous hydrogen peroxide solution. For example, through the use of sodium bicarbonate or ammonium bicarbonate solutions in preconditioning the anionic exchange resins, a significant amount of sodium remains on the treated resin. Thus, when the hydrogen peroxide solution is brought into contact with the pretreated anionic exchange resin, the solution becomes contaminated with sodium.
Additionally, metal contaminants in the resin may contribute to the accelerated decomposition of hydrogen peroxide solution. Decomposition of the solution can be particularly problematic as a result of the exothermic nature of the reaction. The temperature near the zone of contact between the resin and the solution can increase very rapidly, increasing the rate of decomposition. This can result in self-accelerating reaction, possibly terminating in an explosion of the purification equipment.
To meet the requirements of the semiconductor processing industry of providing an ultra-pure hydrogen peroxide solution and to overcome the disadvantages of the related art, it is an object of the present invention to provide novel methods of preconditioning a resin useful in the removal of ionic impurities from a hydrogen peroxide solution the methods can be carried out in a facile and cost effective manner. The invention has particular applicability to preconditioning resins used in the removal of sodium and metal contaminants.
It is another object of the invention to provide resins prepared by the novel preconditioning methods.
It is a further object of the invention to provide methods of removing ionic contaminants from a hydrogen peroxide solution using resins prepared by the novel preconditioning methods.